#include "apue.h"
#include <fcntl.h>

int main(int argc, char* argv[])
{
    int val;
    if (argc != 2)
        err_quit("usage: a.out <descriptor#>");
    if ((val = fcntl(atoi(argv[1]), F_GETFL, 0)) < 0)
        err_sys("fcntl error for fd %d", atoi(argv[1]));

    switch (val & O_ACCMODE) // O_ACCMODE<0003>：读写文件操作时，用于取出flag的低2位
    {
    case O_RDONLY:
        printf("read only");
        break;
    case O_WRONLY:
        printf("write only");
        break;
    case O_RDWR:
        printf("read write");
        break;
    default:
        err_dump("unknown access mode");
    }

    if (val & O_APPEND) printf(", append");
    if (val & O_NONBLOCK) printf(", nonblocking");
    if (val & O_SYNC) printf(", synchronous writes");

# if !defined (_POSIX_C_SOURCE) && defined (O_FSYNC) && (FSYNC != O_SYNC)
    if (val & O_FSYNC) printf(", synchronous writes");
# endif    
    putchar('\n');
    exit(0);
}
